An electron gas refers to a collection of free electrons that move independently within a material, typically in metals. These electrons are not bound to any specific atom, allowing them to conduct electricity and heat efficiently. The behavior of an electron gas can be described using statistical mechanics, which helps in understanding properties like conductivity and thermal behavior. In solid-state physics, the concept of an electron gas is crucial for explaining phenomena such as Fermi energy and band theory. The electron gas model simplifies the complex interactions between electrons and ions in a solid, making it easier to analyze the electronic properties of materials like copper and aluminum.